Hummingbird

Fully
one-third of a hummingbird's body weight is in its chest muscles, which
power its wings.

Hummingbirds
have the largest heart for their body size of any animals. This makes
sure a rich supply of oxygen and nutrition are always flowing through
the body.

Hummers
can allow their core body temperature to drop dramatically when asleep
at night or sometimes during daytime naps. This conserves energy so
they won't starve while they sleep.

The body
shape is close to spherical, helping the hummer to conserve energy,
and fluffy body feathers hold the bird's body heat in.

The tiny
legs and feet simply cannot walk. They work just fine at clinging to
thin twigs and branches. Hummingbirds are tiny enough to fit into tiny
spaces even when their wings are spread in flight, and their unique
ability to fly straight up, straight down, and backward makes walking
unnecessary. Having tiny legs and feet improves their flight by making
their bodies more streamlined and light.

Hummingbirds
eat a mostly liquid diet, so their bodies do not usually need to conserve
water. Unlike all other birds, hummingbird urine is usually made up
of the same clear, yellowish liquid, urea, that mammals produce.
So it's hard to find "whitewash" anywhere around a hummer
perch. (The urine produced by birds in other families is chalky and
whitish because it's made up of uric acid, which helps them to conserve
water.)